Laboratorio 1

A second, more precise flowchart takes debounce into account, implementing a delay to check

the previous state of the button and determine if an action on the button has occurred.

Then we moved on to the configuration:

• PA5 (led) in output mode;

• PC13 (pushbutton) in input mode.

Using the manual, we identified the following HAL functions to be used:

• HAL_GPIO_ReadPin to read the value of a pin;

• HAL_GPIO_WritePin to set the value of a pin;

• HAL_GPIO_TogglePin to switch the status of the pin;

• HAL_Delay to introduce a delay in milliseconds.

We proceeded to write the C code and added it to the “USER code” sections of the

automatically generated code in the IDE.

#include "main.h"

uint32_t debounce_time = 20; // Debounce time in milliseconds

int main(void){

while (1)

{ // Check if the button is pressed (transition from high to low)

if (HAL_GPIO_ReadPin(GPIOC, GPIO_PIN_13) == 0)

{ // Small delay to handle debounce

HAL_Delay(debounce_time);

// Confirm that the button is still pressed after debounce delay

if (HAL_GPIO_ReadPin(GPIOC, GPIO_PIN_13) == 0)

{ // Toggle the LED state

HAL_GPIO_TogglePin(GPIOA, GPIO_PIN_5);

}

}

}

}

Note: The pushbutton has a logic level of "0" when pressed.

Testing the program on the board empirically demonstrated the correct operation of the

exercise.

2.2 Varying blinking frequency

The goal of this exercise is to create a program that progressively increases the LED's blinking

frequency with each button press. After a reset, the LED should blink at a frequency of 0.25 Hz.

If the frequency exceeds 8 Hz (a limit set by us), the program resets to its initial state.

First, we implemented the flowchart:

The flowchart checks if the pushbutton is pressed. If so, the frequency is doubled. If the

imposed limit is exceeded, the program resets. The variable TOGGLING_PERIOD accounts for

debounce in frequency calculation when the button is pressed, while it remains equal to

LED_PERIOD otherwise.

Using the same method, we continued with the configuration, which was identical to the

previous exercise.

Then, we implemented the code:

#include "main.h"

// Initialize variables

uint8_t reset_state = 1; // Start in reset state (LED off)

uint32_t led_period = 4000; // Initial LED period in milliseconds

uint32_t debounce_time = 20; // Debounce time in milliseconds

uint32_t toggling_period; // Initialize toggling period to initial value

int main(void)

{ while (1)

{ // Check if the button is pressed and was previously released

if (HAL_GPIO_ReadPin(GPIOC, GPIO_PIN_13) == 0) {

HAL_Delay(debounce_time); // Debounce delay

// Check the button state again after the delay

if (HAL_GPIO_ReadPin(GPIOC, GPIO_PIN_13) == 0) {

if (reset_state == 1) {

// Exit reset state

reset_state = 0;

led_period = 4000; // Restore initial period

}

else {

// Halve the period and check the limit

led_period *= 0.5;

if (led_period < 125) {

reset_state = 1; // Enter reset state

}

}

}

toggling_period = led_period - debounce_time; // Update toggling period

}

// LED toggling logic

if (reset_state == 1) {

// Reset state: keep the LED off

HAL_GPIO_WritePin(GPIOA, GPIO_PIN_5, 0);

}

else {

// LED toggling logic

HAL_GPIO_TogglePin(GPIOA, GPIO_PIN_5);

HAL_Delay(toggling_period);

toggling_period = led_period; // Reset toggling period

}

}

}

Testing the program revealed a limitation of the polling method: the code is unresponsive to the

button during delays introduced by the HAL_Delay() function.

2.3 Generating a Square Wave

The objective of this exercise is to generate a square wave with a frequency of 500 Hz on PINA10

and observe it on an oscilloscope.

We started by generating the flowchart:

Then we moved on to the configuration:

• PA10 in output mode.

And then to the implementation of the code:

#include "main.h"

uint32_t led_period = 2; // LED blink period (ms)

int main(void)

{

while (1)

{ // LED blinking

HAL_GPIO_TogglePin(GPIOA, GPIO_PIN_10);

HAL_Delay(led_period);

}

}

The pin's signal was connected to the oscilloscope using the board's Morpho headers.